Preheat oven to 400 degrees; line a baking sheet with parchment paper or foil. On a lightly floured work surface, unfold pastry; roll out to a 12-by-14-inch rectangle. Place on sheet; refrigerate.
In a large skillet, melt butter over medium; reserve 1 tablespoon in a small bowl. To skillet, add apples, 1/2 cup sugar, and cinnamon. Increase heat to medium-high; cook, tossing occasionally, until apples are tender and liquid has evaporated, about 15 minutes. Spread filling on a second rimmed baking sheet; let cool completely.
With one short side of dough facing you, mound filling horizontally in a strip across the center, leaving a 1-inch border on both long sides. Fold top part, then bottom part of dough over filling. Turn pastry over, seam side down.
Brush pastry with reserved melted butter; sprinkle with remaining 2 tablespoons sugar. Using a paring knife, cut steam vents in center of pastry. Bake until golden brown, 35 to 40 minutes. Let rest 10 minutes before serving.